The disclosed invention relates to the field of the optical storage of digital data, and in particular, to the use of diode lasers to read or write data in an information storage and retrieval device.
In high speed random access optical recording systems, it is well known to use a modulated and focused radiation beam, usually a laser, to record both digital and analog information on a recording surface. See e.g., U.S. Pat. No. 3,314,073, issued to Becker on Apr. 11, 1967, wherein a modulated laser beam is focused on to a light sensitive media. Since all optical recording systems which make use a focused coherent light beams operate using the same physical principals, most optical recording systems also have certain basic elements in common. For example, all systems must have a means for focusing the incident read beam on the disk surface, some means for tracking the read beam over the disk surface, and a means of detecting the data recorded on the disk surface, whether reflected by the surface toward a detector system or transmitted through the system to a detector, see e.g., U.S. Pat. No. 3,991,275, issued Nov. 9, 1976, to Buithius.
In recent years, there has been increased interest in the development of optical storage devices which can record as well as read optical information. See e.g. U.S. Pat. No. 4,363,116, issued Dec. 7, 1982, to Kleuters et al., wherein a single laser is used to both record data on, and to read data from, the disk surface. In Kleuters, this dual purpose is accomplished by switching the laser from a higher intensity write beam to a lower intensity read beam. There has also been increased interest in the use of multi-laser systems for both reading and writing. See U.S. Pat. No. 4,198,701, issued Apr. 15, 1980, to Reddersen et al., wherein a first beam is used for writing data, and a second beam is used for reading data. See also U.S. Pat. No. 4,334,299, issued June 8, 1982, to Komurasaki et al.
In the early optical recording devices, gas lasers were used to read and write data. In recent years, the power output of semiconductor lasers has increased and sustained performance has become more reliable. See U.S. Pat. No. 4,360,920, issued Nov. 23, 1982 to Woda et al.; and U.S. Pat. No. 4,360,919, issued Nov. 23, 1982, to Fijiwara et al. As a result, diode lasers has begun to be used in optical recording devices to read and, more recently, to write user data. See for example U.S. Pat. No. 4,345,321, issued Aug. 17, 1982 to Arquie et al.
However, the performance characteristics of diode lasers still vary widely from individual laser to individual laser. Accordingly, where standardized output for reading or writing is required, it has been necessary to custom design the optics in the device according to the specific output characteristics of the individual laser diode mounted in the device. See U.S. Pat. No. 4,322,838, issued Mar. 30, 1982, to Neumann, disclosing a collimating system; U.S. Pat. No. 4,333,173, issued to Yonezawa et al., and; U.S. Pat. No. 4,128,308, issued Dec. 5, 1978 to McNaney. Thereafter, should that laser need to be replaced, the optical elements which compensated for the output characteristics of that diode would also need to be changed or adjusted. It is difficult and expensive to make such matching changes and adjustments in a field location in order to bring the output of the new diode laser into specification. Even if the replacement laser characteristics are known and the appropriate optical elements on hand, the alignment of the element relative to the laser requires extremely precise testing procedures and equipment.
The disclosed invention addresses this problem by providing a field replaceable laser diode module having customized and precisely aligned elements mounted thereon to produce standardized laser output. The module can easily and efficiently be replaced in a field maintenance environment and a defective laser can be replaced in the field without undue or expensive adjustments. Additionally, closer tolerances can be maintained by adjusting the modules during manufacture at the factory where permanent manufacturing and testing facilities can be utilized.
It is an object of this invention to provide a diode laser module which is field replaceable.
It is another object of the disclosed invention to provide a diode laser module which is pre-tuned to standard, reproducible specifications.
It is yet another object of the disclosed invention to provide a diode laser unit which can be easily replaced in a field location.